Demountable printing cylinders

ABSTRACT

A demountable plate cylinder for printing presses, the cylinder being shrunk-fit on a mandrel formed of a metal having a relatively low thermal coefficient of expansion. Fitted into the ends of the cylinder are end closures having heat-expandable bores through which the mandrel is extended. In order to minimize the time required to effect assembly and disassembly and also to avoid overheating the cylinder when heat is applied to the exposed faces of the end closures to expand the bores, the mass of the outer region of each closure is relieved, whereby thermal energy is conducted mainly toward the inner or hub region surrounding the bore.

United States Patent n 1 Katz [451 Dec. 17, 1974 85,544 2/1936 Sweden 29/123 Primary Examiner-Alfred R. Guest [57] ABSTRACT A demountable plate cylinder for printing presses, the

cylinder being shrunk-fit on a mandrel formed of a 8 Claims, 7 Drawing Figures DEMOUNTABLE PRINTING CYLINDERS [75] Inventor: Sidney Katz, Spring Valley, N.Y. [73] Assignee: Mosstype Corporation, Waldwick,

[22] Filed: Sept. 25, 1973 [21] Appl. No.: 400,685

[52] US. Cl. 29/123 [51] Int. Cl B2111 31/08 [58] Field of Search 29/123 [56] References Cited UNITED STATES PATENTS 1,801,396 4/1931 Thatcher 29/123 X 2,787,956 4/1957 Kirby et a]: 29/123 X FOREIGN PATENTS OR APPLICATIONS 727,992 4/1955 Great Britain 29/123 PATENTE' DEB] 7 I974 SHEET 2 BF 2 BACKGROUND OF THE INVENTION This invention relates generally to plate cylinders for printing presses, and more particularly to an improved demountable cylinder for this purpose.

In the flexographic process, printing is effected by rubber printing plates mounted on cylinders, the paper to be printed being impressed on the inked printing plates. The cylinder is provided with an integral shaft of a length appropriate to the printing press for which it is intended. A preferred form of a rubber plate cylinder is that disclosed in US. Pat. No. 2,787,956 in which a cylinder fabricated of magnesium, is shrunk-fit on a shaft or mandrel of steel. Thus the cylinder has a high thermal coefficient of expansion relative to that of the mandrel.

When heat is applied to the ends of the cylinder, the bores thereof expand rapidly to permit the shaft tobe inserted. Upon cooling, the bores contract to their original size to bring about an immovable union between the mandrel and cylinder. Withdrawal of the shaft is accomplished merely by again applying heat to the cylinder ends. Since expansion and contraction of each bore remains constant and occurs uniformly around its circumference in the same degree, neither'wear nor physical change takes place on either mating surface. As a consequence, the assembly and disassembly procedure can be carried out repeatedly over the full life of the cylinder.

Because demountable cylinders of the type disclosed in the above-noted patent are interchangeable from press to press regardless of the width or make of the press, it is possible to get along with fewer cylinders. A single shaft or mandrel can be used for the full range of cylinder diameters on any given press. Likewise, a single cylinder will fit shafts of different lengths. The demountable cylinder has many practical advantages over integral-shafted cylinders. Because the magnesium cylinders are much lighter than steel cylinders, they can be handled without difficulty and cost less to ship. And because these cylinders take up less space than shafted cylinders, they are more readily stored.

A practical problem is encountered in using existing forms of demountable cylinders whose outside diameter is 7 inches or greater, for then a substantial time is First, because heat must be applied for a time sufficient to cause the required degree of bore expansion, a relatively prolonged period is involved to reach this point, for much of the applied heat is diverted to the outer region where it is wasted. Thus the time of assertibly and disassembly of medium and large diameter cylinders is fairly long, which is objectionable in plant operations.

required to heat up the end closures of the cylinders to cause the bores therein to expand to allow removal or insertion of the mandrel. The standard end closure is in collar form, the outer diameter of the collar matching the inner diameter of the cylinder end intowhich the closure is to be fitted whereas the inner diameter of the collar, regardless of the associated cylinder size, is always the same. Hence for a medium or large diameter cylinder, the metal body of the collar is relatively massive.

When, therefore, heat is applied to the exposed face of the standard end closure dimensioned for a large diameter cylinder, thermal energy is conducted by the body of the collar to the inn'er or hub region surrounding the bore thereby causing the bore to expand. But not all of the applied energy serves this useful purpose, for a considerable portion thereof is wasted in that thermal energy is also conducted toward the periphery of the closure through the large, outer region thereof adjacent the inner surface of the cylinder. This dissipation of energy gives rise to two drawbacks.

Second, because much of the applied heat is transferred by the closures to the ends of the cylinders, this tends to raise the cylinder temperature. This may be damaging to, printing plates and other components located on the cylinder surface which cannot tolerate elevated temperatures.

While improved heat transfer can be effected byan end closure having a spoked wheel rather than a solid collar configuration to reduce conduction toward the outer region of the closure and thereby cut down the time necessary to expand the bore diameter, this improvement is at the expense of the structural integrity and torque capacity of the closure. Torque tests indicate that a spoked wheel closure has a torque capacity of about 80 percent of that of a standard solid collar closure having the same bore size.

SUMMARY OF THE INVENTION In view of the foregoing, it is the main object of this invention to provide an improved printing plate cylinder capable of being mounted and demounted on a mandrel by a shrink-fitting operation, the cylinder including end closures adapted to facilitate this operathe bore when heat is applied without, however, sacrificing the structural integrity and torque capacity of the closure. Another advantage of the invention is that the end closure serves to conduct most of the applied heat to the annular hub region surrounding the bore, so that relatively little heat is conducted toward the outer region and overheating of the cylinder end surrounding the outer region is obviated.

Also an object of the invention is to provide an end closure for printing plate cylinders which may be fabricated at relatively low cost.

Briefly stated, these objects are attained in an end closure for a demountable printing plate cylinder, the end closure being constituted by a heat-expandable collar whose inner diameter at ambient temperature is slightly smaller than the outer diameter of a mandrel extending therethrough whereby the mandrel is firmly engaged by the collar, the outside diameter corresponding to the inner diameter of the end of the cylinder into which the closure is fitted, the collar being provided with a hub projection adapted to support a heating element which applies heat to the front face of the collar.

The collar is formed with a solid hub region encircling the bore, the outer region of the collar being relieved by an annular channel formed in the rear face thereof which reduces the mass of the outer region whereby thermal energy applied to the front face is mainly conducted to the hub region to rapidly expand the bore and relatively little heat is conducted to the outer region, thereby avoiding the waste of heat and preventing overheating of the cylinder.

OUTLINE OF THE DRAWING For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description of the invention to be read in conjunction with the accompanying drawing wherein:

FIG. I is a perspective view of a demountable cylinder provided with end closures in accordance with the invention;

FIG. 2 is a perspective view of a mandrel which is insertable into the bores of the cylinder shown in FIG. 1;

FIG. 3 is a perspective view of the end closure removed from the cylinder;

FIG. 4 is a longitudinal section taken through the end closure which is fitted within an end of the cylinder;

FIG. 5 is a front view of the end closure;

FIG. 6 is a perspective view of a heater element adapted to cooperate with the end closure; and

FIG. 7 is a sketch illustrating the conduction paths of thermal energy applied to the end closure.

DESCRIPTION OF THE INVENTION Referring now to FIGS. l and 2, there is shown a demountable cylinder constituted by a metal tube 10' of uniform outside diameter having end closures 11 secured thereto. These end closures which are in accordance with the invention are separately cast and machined, and after fabrication the closures are secured by welding or other suitablemeans to the opposite ends of the tube which is relatively thin walled. Metal tube 10 may be made of magnesium, aluminum or any other suitable. material. I

Each end closure is formed with a central throughbore 12 which is coaxial with the tube and has a diameter which at ambient temperature is slightly less than that of a mandrel 13 which extends therethrough whereby the mandrel is firmly gripped by the end closures. End closures 11 are made of a relatively highstrength, low-weight material which is preferably magnesium whose thermal coefficient of expansion is high with respect to the thermal coefficient of expansion of mandrel 13, the latter being preferably made of steel. In practice, closures 11 may be made of aluminum. Thus the mandrel functions as a shaft for the demountable cylinder.

When it is desired to remove the cylinder from the mandrel, it is only necessary to heat the end closures to a degree enlarging the through-bores with respect to the mandrel to unlock the connection therebetween'. That is to say, the'heat applied to these closures'effects physical expansion of the enclosures thereby enlarging the through-bores and releasing the mandrel to permit free sliding movement of the end closures along the mandrel.

Though the end closures serve to conduct heat to the mandrel which also causes the mandrel to expand, the expansion of the end closures is greater than that of the mandrel, in that the diameter of the bores, which is initially slightly less than the diameter of the mandrel becomes slightly larger than the diameter of the mandrel.

As best seen in FIGS. 3 to 5, each end closure 11 has a collar-like formation. The inner diameter of the collar determines the bore size. The outer diameter of the col lar matches the inner diameter at the end of the tube 10 into which the closure is fitted. It will be seen that the end of the tube is machined to form a shoulder section to accommodate the collar.

In practice, in order to provide demountable cylinders with mandrels or shafts suitable for various types of presses, the cylinders are provided with end closures in a range of sizes, such as a 2 /2 inch diameter bore, a 3 /2 and a 4 V2 inch diameter bore. Each bore size has a different diameter hub (to be later described) and a correspondingly sized expander to fit the hub for applying heat to the end closure.

Projecting from the front face of the end closure is a circular hub 14, the junction of the hub and the end face defining an annular groove 15. This groove is adapted to accommodate the complementary semicircular, heating plates 16 and 17 of an expander of the type shown in FIG. 6. The expander includes a pair of curved frames 18 and 19 which are pivoted together at one end, the other ends .of the frames having handles 20 and 21 extending therefrom to facilitate clamping the expander about the hub. Within the frames are heater elements electrically energized through acable 22 connectable to a power line.

The mass of the end closure is relieved by means of I an annular channel 23 formed in the rear face thereof.

. out, whereas the outer region which begins at the I much more energy is conducted toward the bore than boundary line, indicated by letter X passing through the inner bank of the channel, and extends to the pe riphery of the end closure, has much less metal because of the channel therein.

The thermal effect of the channel on the behavior of the end closure will now be described in connection with FIG. 7. It will be seen that heating plate, 16 of the expander is seated within groove 15 of hub 14 and lies against the front face of the end closure 11 to apply heat thereto. As indicated by the arrows, thermal energy applied to the front face is transferred by the metal in the inner or hub region of the closure to throughbore 12. Thermal energy is also conducted by the outer region of the closure to the end of cylinder tube 10.

Because the outer region is relieved by channel 23,

toward the cylinder 10, hence, the bore expands quickly to a degree sufficient to insert or withdraw the mandrel well before the heat reaching the cylinder tube has raised the temperature thereof to an unacceptable level. Thus the heat transfer path to the cylinder tube is effectively throttled by the reduced transverse area of the closure radially outward from the axis to minimize the waste of energy.

Because the solid hub region surrounding the bore is the region which engages the mandrel, the fact that the outer region is relieved does not significantly impair the torque capacity of the closure, for the torque capacity of the relieved closure is virtually the same as a closure which is solid throughout its body. Hence the structural integrity and torque capacity of the closure is not adversely affected by the channel, whereas its thermal transfer characteristics are improved considerably.

While there has been shown a preferred embodiment of demountable printing cylinders in accordance with the invention, it will be appreciated that many changes may be made without departing from the essential spirit of the invention.

I claim:

1. A demountable printing cylinder adapted to be shrunk fit by means of a flat annular heating element onto a mandrel formed of metal having a relatively low thermal coefficient of expansion; said cylinder comprising:

an open-ended tube, and end closures disposed at opposite ends of said tube, each closure having a collar-like formation defining annular front and rear faces, an inner region surrounding a central bore through which the mandrel is extended and an outer region whose periphery engages the associated end of said tube, said outer region being relieved in the rear face of the closure to reduce the mass thereof whereby thermal energy applied to said closure by means of said annular heating plate engaging substantially the entire front face thereof is transferred mainly to said inner region to expand said bore at a rapid rate, only a minor portion of said heating energy being transferred by said relieved outer region to said tube, said closure being formed of a metal having a relatively high thermal coefficient of expansion.

2. An arrangement as set forth in claim 1, wherein said mandrel is formed of steel.

3. An arrangement as set forth in claim 1, wherein said closure is formed of magnesium.

4. An arrangement as set forth in claim 1, wherein said heating element is formed by a pair of complementary semi-annular plates and said closure is formed with a circular hub projecting from the front face thereof, the junction of the hub and front face defining an annular groove adapted to receive the arcuate edges of the plates forming said heating element whereby said plates engage said front face.

5. An arrangement as set forth in claim 1 wherein said outer region is relieved by an annular channel formed in the rear face of the closure.

6. An arrangement as set forth in claim 1 wherein the opposite ends of said tube have shoulders formed therein to nest said closures.

7. An arrangement as set forth in claim 1, wherein said closures are welded to said ends.

8. An end closure for a demountable cylinder, said end closure being adapted to be heated by a heating element formed by a complementary pair of semiannular plates and having a collar-like formation provided with annular front and rear faces to define a central bore through which a mandrel is extendible, a solid hub region surrounding the bore and an outer region having a relieved portion in the rear face thereof to reduce the thermal conductivity thereof, and a hub projecting from the front face of the closure, the junction of said hub and said front face defining an annular groove to receive the arcuate edges of said pair of semiannular plates whereby said plates lie in contact with said annular front face. 

1. A demountable printing cylinder adapted to be shrunk fit by means of a flat annular heating element onto a mandrel formed of metal having a relatively low thermal coefficient of expansion; said cylinder comprising: an open-ended tube, and end closures disposed at opposite ends of said tube, each closure having a collar-like formation defining annular front and rear faces, an inner region surrounding a central bore through which the mandrel is extended and an outer region whose periphery engages the associated end of said tube, said outer region being relieved in the rear face of the closure to reduce the mass thereof whereby thermal energy applied to said closure by means of said annular heating plate engaging substantially the entire front face thereof is transferred mainly to said inner region to expand said bore at a rapid rate, only a minor portion of said heating energy being transferred by said relieved outer region to said tube, said closure being formed of a metal having a relatively high thermal coefficient of expansion.
 2. An arrangement as set forth in claim 1, wherein said mandrel is formed of steel.
 3. An arrangement as set forth in claim 1, wherein said closure is formed of magnesium.
 4. An arrangement as set forth in claim 1, wherein said heating element is formed by a pair of complementary semi-annular plates and said closure is formed with a circular hub projecting from the front face thereof, the junction of the hub and front face defining an annular groove adapted to receive the arcuate edges of the plates forming said heating element whereby said plates engage said front face.
 5. An arrangement as set forth in claim 1 wherein said outer region is relieved by an annular channel formed in the rear face of the closure.
 6. An arrangement as set forth in claim 1 wherein the opposite ends of said tube have shoulders formed therein to nest said closures.
 7. An arrangement as set forth in claim 1, wherein said closures are welded to said ends.
 8. An end closure for a demountable cylinder, said end closure being adapted to be heated by a heating element formed by a complementary pair of semi-annular plates and having a collar-like formation provided with annular front and rear faces to define a central bore through which a mandrel is extendible, a solid hub region surrounding the bore and an outer region having a relieved portion in the rear face thereof to reduce the thermal conductivity thereof, and a hub projecting from the front face of the closure, the junction of said hub and said front face defining an annular groove to receive the arcuate edges of said pair of semi-annular plates whereby said plates lie in contact with said annular front face. 